Verifying memory for BGP routing table

[cable_tech]

Hi can someone please advise on how to verify if a router has sufficient memory to take a full internet routing table.

I know you need at least 128M RAM, but when i do a " show version " i am unsure how to interpret all the different memory figures.

Thanks

[Georg Pauwen]

Hello,

the memory consumption by BGP routes depends on the number of attributes such as multi-path support, soft reconfiguration, number of peers, and AS_PATH.

You might want to check this document, it talks in detail about the memory consumption of BGP:

Achieve Optimal Routing and Reduce BGP Memory Consumption

http://www.cisco.com/en/US/tech/tk365/tk80/technologies_tech_note09186a0080094a83.shtml

HTH,

GP

[cable_tech]

Thanks, the document looks good. Can you help with the interpretation of the show version command to verify how much RAM is in a router.

[akshri · Accepted solution]

Hi,

You will find similar kind of string in ur sh version command as follows.

"cisco 7206VXR (NPE400) processor with 245760K/16384K bytes of memory."

Now,

245760K + 16384K= 262144K

RAM capacity = 262144K/1024 = 256M

so the RAM is 256MB.

Hope this helps.

Amit

[konigl]

I have seen a Catalyst 6509 with MSFC and 128MB take the full BGP route table; but CEF ended up being disabled because the box was short on memory.

It might be different with a router and 128MB memory, but I think you should consider 256MB as the minimum for full BGP tables these days.

[cable_tech]

Hi akshri,

Thanks for the reply. Can you also tell me why you divided by 1024 to get the RAM capacity. Where did you get the 1024 from.

[thisisshanky · Accepted solution]

Memory is measured in bytes, Kilobytes or Megabytes (can use gigabytes too)

1 Kilobyte = 1024 Bytes.

1 Megabyte = 1024 Kilobytes.

Now the number 245760K/16384K = 245760KB+16384KB= 262144KB. The value is in Kilobytes. To convert this into Megabytes, you need to divide this number by 1024. (see above conversion table)

So 262144 KB = 262144/1024 = 256MB.

Hope thats clear.

[cable_tech]

Ver clear, thanks for the info.